Balance ring for pulsating fluid machinery



Feb. 25, 1964 J. O. BYERS, JR

BALANCE RING FOR PULSATING FLUID MACHINERY Original Filed March 5, 19583 Sheets-Sheet 1 UTE-l INVENTOR.

Feb. 25, 1964 J. o. BYERS, JR 3,122,104

BALANCE RING FOR PULSATING FLUID MACHINERY Original Filed March 5, 19583 Sheets-Sheet 2 INVENTOR.

Jen/5 dfiyms, J4.

United States Patent 3,122,194 eALANcE mun eon rursa'rmc ramp MAcnrNenvJames 0. Byers, In, Oalrville, Conn, assignor to The Bendix Corporation,St. Joseph, Mich, a corporation of Delaware Continuation of abandonedapplication Ser. N 719,285, Mar. 5, 1958. This application Dec. 23,1.961, Ser. No.

1 (1mm. c1. 103-161) The present invention relates to rotating fluidhandling devices having two parts which rotate relative to each otherand which have end surfaces through which the axis of rotation passesand which are forced apart by fluid pressure forces; and moreparticularly to fluid pressure actuated balancing means for holdingsliding sealing valving surfaces formed on the end surfaces of tworelatively rotating parts into engagement with each other with agenerally predetermined force. The present application is a continuationof US. application Serial No. 719,285 filed March 5, 1958, nowabandoned.

The present invention has particular advantages in positive displacementhydraulic pumps and motors of the type having a casing member and aninternal member which are relatively rotatable about an axis whichpasses through abutting end valving surfaces on the respective members,and which valving surfaces are biased apart by pressure of the fluidpassing through the valving surfaces. In the usual design of pumps andmotors of this type, the internal member is usually made the rotatingmember and is provided with a plurality of radially extending cylindershaving pistons therein which reciprocate when the interned member isrotated. In such an arrangement fluid is usually added to and exhaustedfrom the rotor, through ports in the end valving face of the rotor, asthese rotor ports are rotated past suction and discharge ports in anabutting valving surface of the casing member. It is inherent in such anarrangement that fluid pressure from the discharge ports flows betweenthe valving surface to bias the valving surfaces apart. An opposingforce must therefore be applied between the rotor and casing members inorder to hold the valving surfaces into sliding sealing engagement witheach other.

It is highly impractical to manufacture rotors with an end to enddimension that provides a suitable sealing fit between two opposite endinternal casing surfaces. Prior art attempts to produce pumps of thisnature, and with which applicant is familiar, have utilized a pluralityof slipper pistons which are biased outwardly of the rotor member intoabutment with one inside face of the casing member to force the otherface of the rotor member into sealing engagement with the oppositeinternal face of the casing member. Individual ones of these pistonshave been communicated with individual ones of the pumping chambers inthe rotor, so that the changing pressure in each purnping chamber willautomatically change he force biasing the sealing surfaces together in amanner slightly greater but proportional to the force tending toseparate the valving surfaces. Prior art structure have been quitecomplicated and expensive to mmufacture, and what is more important havenecessitated the expenditure of considerable power loss in rotating theplurality of individual slipper pistons over their abutting bearingsurface.

An object of the present invention is the provision of a new andimproved fluid handling device of the character above referred to whichis greatly simplified in its construction, which is more eflicient inits operation, and is cheaper to manufacture than prior art structures.

Another object of the present invention is the provision of a new andimproved pump and/ or motor of the above described type whose mechanicalefliciency is considerably improved over prior art structures.

3,122,104 Patented Feb. 25, 1964 ice The invention resides in certainconstructions and combinations and arrangements of parts; and furtherobjects and advantages will become apparent to those skilled in the artto Which the invention relates from the following description of thepreferred embodiment described with reference to the accompanyingdrawings forming a part of this specification, and in which:

FIGURE 1 is a cross sectional view taken approximately on the line 11 ofFIGURE *3 of a hydraulic pump embodying principles of the presentinvention;

FIGURE 2 is a cross sectional view taken approximately on the line 22 ofFIGURE 1;

FIGURE 3 is an end view of the pump shown in FIG- URE 1 having partsbroken away and sectioned and is taken approximately upon the line 33 ofFIGURE 1;

FIGURE 4 is an end View of a porting plate shown in FIGURES 1 and 2; and

FIGURE 5 is a cross sectional view taken approximately on the line 55 ofFIGURE 4.

While the invention may be otherwise embodied, it is herein shown anddescribed as embodied in a positive dislacement hydraulic pump capableof producing pressures in the neighborhood of approximately 1,500 p.s.i.The pump is intended for use in the central hydraulic systems of farmtractors and the like.

The pump shown in the drawing generally comprises an outer casing memberA having an internal chamber 10 therein containing a radially inwardlyfacing annular camming surface 12; and an inner member B having aplurality of radially outwardly extending cylinder bores 14 in whichindividual pistons 16 are positioned in a manner to be reciprocated bythe camming surface 12 during relaive rotation of the inner and outermembers. The casing member in the present instance is a stationary one,and the internal member B is adapted to be rotated relative to thecamming surface 12 by an axially positioned shaft 18 which extendsthrough one end wall 20 of the casing member A. The inner end of theshaft 18 is journaled in a sleeve bearing 22 that is supported in anaxial bore 24 in the opposite end wall 26 of the casing member A; andthe projecting end of the shaft 13 is suitably journaled and sealed withrespect to the end wall 26. The center portion of the shaft is suitablesplined to the inner rotor member B substantially on the radial planepassing through the cylinder bores 14.

Each of the individual pistons 16 are provided with a ball 28 forengagement with the camming surface 12; and upon rotation of the shaft18, centrifugal force causes the individual pistons 16 to be biasedradially outwardly into firm engagement with the camming surface 12.Relative rotation between the inner and outer members causes the pistons16 (of which there are 6 in the present pump) to be reciprocated intheir cylinder bores 14. By properly communicating each cylinder bore 14to a supply of fluid at suction pressure when its piston 16 is movingradially outwardly, and by properly communicating each cylinder bore tothe discharge passages of the pump when its piston 16 is moving radiallyinwardly, a pumping action is established. By successively valving eachof the cylinder bores to the suction and discharge connections of thepump during their respective suction and discharge strokes, a continuousfiow of fluid is achieved.

Inasmuch as the position and duration of the suction and dischargestrokes for each cylinder are fixed by the configuration of the cammingsurface 12; and inasmuch as the camming surface is held stationary withrespect to the casing member A, the start of the suction stroke for eachcylinder will take place when each cylinder moves into precisely thesame position relative to the casing member A, and will continue overprecisely the same circular arc of the casing member. Likewise, thedischarge stroke for each cylinder starts when each moves 3. intoprecisely the same position and continues over the same circular arc ofthe casing member. Fluid can be added to and taken from each of theindividual cylinders to suction and discharge passages in the casingmember when the cylinders are properly positioned in the hous ng memberrelative to the camming surface 12.

The pump shown in the drawing has a generally elliptically shapedcamming surface 12, so that each individual cylinder has two pumpingcycles during each revolution of the rotor member B. Valving of eachindividual pumping cylinder to the suction and discharge connections ofthe pump is accomplished by a rotary disc valve arrangement formedbetween one end of the rotor member B and the 7 end wall 26 of thecasing member A. The rotary disc valve arrangement shown generallycomprises a pair of matching valving surfaces which slidingly sealinglyengage each other, and one of which surfaces 36 is formed in and rotatedby the rotor member B while the other valving surface 32 is supported onthe casing member A. In order that sealing angular alignment of thesesurfaces can be accomplished easily when the pumps are made on a massproduction basis, the matching valving surfaces 3% and 32 arespherically shaped; and in order that the valving operation can beadjusted relative to the camming surface to vary the discharge of thepump (as will later be described),

the valving surface 32 is formed as a surface of a porttion 38 of thepump to be distributed through an annular groove 49 in the end wall 26to the internal chamber 16 p of the pump. The valving surface 39 of therotor member B is provided 'with a plurality of identically shapedcircular ports 42 each of which communicate with a re spective cylinderbore 14; and these ports 42 are uncovered by the port plate 36 to permitfluid from the internal chamber 19 to be drawn into the cylinder boresduring their suction strokes. The ports 42 must, therefore, be sealedoff from the internal chamber 14 during their discharge strokes; andinasmuch as the camming surface 12 causes these discharge strokes to beproduced over two diametrically opposite 90 arcs, the port plate 36 hasan hour glass type of configuration, as best seen in FIG- URES 2 and 4,capable of sealing off the ports 42 from the internal chamber over twodiametrically opposite 90 arcs. V V

' Referring now to FIGURE 2 of the drawings, the port plate 36is showntherein in its position providing maximum displacement for the pump.Assuming counter clockwise rotor rotation as seen in FIGURE 2, thepistons 16 start their discharge strokes when the center line of theircylinder bores 14 become coincident with the major axis 44 of thecamming surface. When the center line of the ports 42 become coincidentwith the major axis 44, the

trailing edge of the ports 42 become coincident vith the;

' after the cylinder bores 14 pass the major 'axis 44-, the

leading edge of the circular ports 42 become coincident withthe leadingedge 50 of an arcuately shaped discharge port 52 that is centrallypositioned within each half of operation of the discharge ports 52 whichcontinues for j approximately 32 of rotor rotation. The leading edge 5t)and the trailing edge 5 of the discharge ports 52 are formed to the same.radiusas the circular ports 42, and about centers'whichare spaced 23 ofrotation; apart so that the circular ports 42 remain full open withrespect to the discharge port 52 for the. next approximately23? the portplate 36. Thereafter subsequent rotation of the 1 rotor member causesthe circular ports to start the opening of rotation. Thereafter theleading edge of the circular ports 42 begin to move past the trailingedge 54 of the discharge port 52; and after approximately 32 of furtherrotation, the trailing edge of the circular ports 42 become coincidentwith the trailing edge of the arcuately shaped discharge port 52 toclose off the ports 42 from both the suction and discharge of the pump.This occurs as the center lines of the individual cylinder bores 14become coincident with the minor axis 56 of the camming surface 12; andthe circular. ports 42 are valved old from both the suction anddischarge of the pump thereafter for approximately 3 of rotor rotation.

The leading edge of the ports 42 become coincident with the trailingedge 58 of the trailing portion 60 of the valving surface 32 after thecylinder bores 14 have moved apprordmately 3 past the minor. axis 56 ofthe camming surface 12; and the individual circular port 42 will remainin communication with the internal chamber 10 or suction passages of thepump until the trailing edge of the ports 42 become coincident with theleading edge 7 46 of the other half of the valving surface 32-whichoccurs when the center line of the cylinder bores 14 become coincidentwith the major axis 44. This completes one suction and discharge cycleas occurs over of rotor rotation; and thereafter'the cycle is repeatedwith respect to the other half of the'porting plate 36 during the second180 of rotor rotation;

The port plate 35 slidably sealingly engages a planar surface 62 in theend Wall 26 of the casing member A in which are located a pair ofdiametrically opposeddischarge ports 64 with which the arcuately shapeddischarge ports 52 of the porting plate always communicate. The ports atare formed by longitudinally drilled passageways 66 which areintersected by a transverse drilling 63 which in turn is intersected *bythe discharge port 70 of the pump.

As previously indicated the port plate 36 is made arcuately movable inorder that the pumps dis lacement,

or quantity of fluid which will be delivered the pump during onerevolution of the rotor, might be varied. By rotating the port plate 36in a clockwise direction from the position shown in FIGURE 2, theindividual circular ports 42 will be valved off by the leading portion43 of the valving surface 32 prior to the time that the radially outwardstroke of the individual pistons 16 have been completed; so that only afraction or" each cylinder bores maximum displacement is filled withfluid from the inlet of the pump. The individual circular ports 42 willthereafter he valved off from both the suction and discharge connectionsof the pump for approximately 3 of rotor rotation; and thereafter theindividual circular ports 42 will be connected with the arcuately shapeddischarge port.

placement of the remainder of 87 of rotation, which will now terminatebefore the cylinder bores 14 reach the minor axis '56. Thereafter theports 42 will be valved olf from both the suction and the discharge ofthe pump .for approximately 3; and'wiil then be communicated with thesuction of the punp during the remaining portion of the discharge strokeof the individual pistons 15. It

1 will be passed to the suction of the pump. By this expediency thetotal quantity of fluid passing the outlet of the pump per rotorrevolution can be varied or controlled by adjusting the angular positionof the porting plate 36 relative to the camming surface 12.

The pump shown in the drawing is provided with automatic means forangularly positioning the port plate 36 in a direction decreasing thedisplacement of the pump when the pressure in its discharge passagesexceeds a predetermined pressure, which in the present instance isapproximately 1,500 p.s.i. The automatic means C for positioning theport plate is best seen in FIGURE 3 of the drawings; and generallycomprises a cylindrically shaped slide member 72 which is positioned ina transverse bore 74 in the cover plate 26. The slide member 72 isnotched out as at 76 to receive a pin 73 that extends through anarcuately shaped opening 86 within the cover plate 26 that communicatesthe bore 74 with the back of the port plate 36. Pin 78 is rigidlyconnected to the port plate 36; and the port plate as is held in itsmaximum displacement producing position, shown in FIGURE 2, when theinner end of the slide member 72 is held into engagement with a shoulder82 formed on the inner end of the transverse bore section 74-. The slide74 is held in this position by a coil spring 84 which is biased againstan abutment plate 85 positioned against the outer end of the slidemember 72 and a closure member 88 which is suitably held in place in theouter end of the transverse bore 74.

The slide member 72 is adapted to be rotated in a direction reducing thedisplacement of the pump by a piston 99 that is positioned in a smallerdiameter bore section 92 in the bottom end of the bore 74; and which inturn is actuated by pressure supplied to its inner surface. Pressureactuation of the piston 96 in turn controlled by a slide valve structure9d which is adapted to communicate the bottom end of the piston 9% tothe suction pressure of the pump until such time as the dischargepressure of the pump reaches a predetermined level of approximately1,508 p.s.i. Thereafter, the slide valve structure 94 is moved tomodulate discharge pressure of the pump to the cylindrical piston 9%causing the slide member 72 to be moved outwardly compressing the spring84 and moving the pin 78 in a direction decreasing the displacement ofthe pump.

The slide valve structure 94 is positioned in a bore @5 which intersectsanother small diameter bore 98 that communicates with the inner end ofthe bore section 92. The slide valve structure is provided with a pairof spaced lands 169 and 102 which when properly positioned will juststraddle the bore 8 and close ed the portions of the bore 95 which lieon opposite sides of the bore 3 from communication with the cylindricalpiston 90. Pressure from the discharge passage 66 is fed through twointersecting bores 104 and 1% to the inner end portion of the bore 96.The outer portion of the bore 96 is communicated with the annularsuction groove 40 by a longitudinal drilling 188; so that either suctionor discharge pump pressures can be communicated to the cylindricalpiston 98 depending upon tire positioning of the slide valve structure94. The slide valve structure 94 is biased inwardly to normallycommunicate suction pressure to the inner end of the cylindrical piston93 by a coil spring 11% which normally holds an abutment plate 112 thatis positioned against the end of the slide valve member 94 intoengagement with the bottom end of the counterbore 116 in which thespring 1 3 is situated. The spring lid is compressed a predeterminedamount by a plug 118 which is forced into the outer end of thecounterbore 116 and suitably held in place. When a predetermined pumpdischarge pressure, which in this instance is approximately 1,500 p.s.i.is delivered to the inner end of the bore 96 the slide valve structure94 is biased outwardly against spring 11%) to cause the abutment plate112 to begin to move out of engagement with the bottom end 114 of thecounterbore 116. This causes the land 1&2 to begin to throttle flowbetween the exhaust drilling 1 53 and the inner end of the cylindricalpiston and inasmuch as some leakage always occurs past the lands 1% and162 discharge pressure from the drilling 1% will flow past land 1150 tothe drilling 93. Inasmuch as outlet flow from the drilling 98 to theexhaust drilling 1&8 is now being throttled, a control pressure isestablished in the drilling 98 which will be of an intensity whichdepends upon the relative overlap being maintained with respect to thelands 1% and 102. A pump discharge pressure of approximately 1,650p.s.i. pressure on the inner end of the slide valve 94 will cause theinner land 1430 to be moved out of overlap with respect to the inner endof the bore 96, and suiiicient pressure is delivered against thecylindrical piston 99 to move the port plate 36 into its no flowposition. At pump discharge pressures between 1,500 p.s.i. and 1,650p.s.i., a proportionate pressure is delivered against the cylindricalpiston 90 to cause the port plate 36 to assume intermediate positions.

Pressure from the arcuately shaped discharge ports 52 in the port plate36 will, of course, tend to flow through the space between the valvingsurfaces 39 and 32 and will tend to bias the valving surfaces apart.Should the surfaces become separated, discharge from the cylinder bores14 will be short circuited directly to the internal chamber 19 therebygreatly decreasing the pumps hydraulic efiiciency. The valving surfaces30 and 32 must therefore be biased together by an amount of force whichwill prevent excessive leakage between the valving surfaces. In orderthat the pressure seepage between the valving surfaces might be confinedto as small an area as possible, and thereby decrease the amount offorce tending to bias the valving surfaces apart, an annular groove 120is formed in the surface 3% a short distance radially outwardly from theradially outer edge of the arcuately shaped discharge ports 52.Similarly an axially positioned recess 122 is formed in the rotor memberB with its radially outer edge positioned a short distance radiallyinwardly from the inner edge of the arcuate shaped discharge ports 52.It will therefore be seen that pressure forces upon the port plate areconfined to its area bounded by the annular groove 120, the axiallypositioned recess 122 and its leading and trailing edges 46 and 58respectively. A full discharge pressure will be exerted against therotor member B on areas defined by the arcuately shaped discharge ports52 and the pressure distribution on the remainder of the area bounded aspreviously set forth, will vary from substantially full pump dischargepressure adjacent the arcuate opening 52 to substantially suctionpressure around the outer edges of the area previously set forth. Anapproximation of the force biasing the valving surfaces apart can beobtained by adding: the force obtained by multiplying the area which isin sliding sealing engagement by a pressure which is approximately onehalf of the difference between suction and discharge pressures, and theforce obtained by multiplying full discharge pressure to the area of thearcuately shaped dis charge ports plus the area of all circular ports 42which are communicated to pressure.

According to principles of the present invention, the valving surfaces36 and 32 are forced into sliding sealing engagement with each otherwith a generally predetermined force by a single annular balancingpiston 124 which extends around the shaft 18. The annular piston 12 ispreferably confined to an area that is as close as possible to the shaft13; and in the embodiment shown in the drawing, is positioned in acounterbore 126 in the end of the opening in the rotor member B throughwhich the shaft extends. O-ring seals 128 and 139 are provided betweenthe annular piston 124 and the sidewalls of the counterbore and shaftrespectively; and another O-ring seal 132 is provided in the shaftopening of the rotor member inwardly from the counterbore 126. The outersurface 134 of the annular piston 124 bears against an annular abutmentor slipper plate 136 which is non-rotatably supported on the end wall 29of the casing member A surrounding the shaft is. Fluid under dischargepres sure is admitted to the inner surface of the annular piston 124 toforce the annular piston into abutment with the slipper plate 136 toproduce a reaction which holds the valving surface 39 of the rotormember B into sealing engagement with the valving surface 32 of the portplate 36. The cross sectional area of the annular piston 12 iispreferably of such a size so as to at all times bias the valvingsurfaces 39 and 32 together by an amount sufficient to prevent excessiveflow between the valving surfaces.

According to further principles of the present invention, pressure issupplied to the counterbore 126 from individual ones of the cylinderbores 14. Inasmuch as the pressure in these cylinder bores variesbetween suction and discharge pressures, a check valve is provided inthese passages to prevent return flow from the counterbore to thecylinder bores during their suction strokes. In the embodiment shown,the interconnecting passageway 138 is counterbored as at 14% adjacentthe bottom of the counterbore 126, and a ball 142 is positioned thereinto prevent the return flow. The depth of the counterbore 140 ispreferably just sufficient to provide from .005 to i010 of an inchclearance between the bottom of the counterbore, such that very littletravel is required of the ball before it is brought into engagement withits seat.

In order to lubricate the sliding surface between the annular piston 124and the slipper plate 136, a pair of concentric annular grooves 144 and146 are provided in the outer surface i34- of the annular piston. Fluidunder pressure from the counterbore 125 flows through a pas sageway 148in the annular piston and then through a groove in the surface 134 whichextends between the recesses 144 and 14a The same pressure that isdelivered against the inner edge of the annular piston 124 is thereforedelivered to the sliding surface between the piston 124 and slipper plat135 to relieve the mechanical bearing forces between these surfaces. Theannular area between the grooves 144 and 146 is sized in such a way thatthe hydraulic forces tending to separate the annular piston 124 from theslipper plate 136 will at all times be slightly less than the forceagainst the end of the annular piston 124 positioned in the counterbore126; and as pre' viously indicated the annular piston 124 is so sized asto hold the valving surfaces 30 and 32 together. Rotation of the annularpiston 124 relative to the shaft 13 is procircular ports 42 in the rotormember B will bein communication with the internal chamber 155 forsubstantial- .ly the full suction stroke of their pistons 15, and untilthe center line of the bores 14 are coincident with the major.

axisedof the camrning surface 12. The ports 42 are valved o& from boththe internal chamber iii and the dis-v charge port 52 for the next 3 ofrotor rotation. At appromately 3 of rotation after the center line ofthe cylinder bores have passed the major axis 44, the circular ports iZbecome communicated with the arcuately'shaped discharge port 52 so thatinward movement of the pistons 3.6 causesiluid to flow out through theports 42, and the 1 oer.

arcu'ately shaped discharge port 52 to one of the discharge ports 64 inthe removable end wall 26 of the casing morn- Inasmuch as the carnmin-gsurface 12 is eliiptically shaped to produce'two pumping cycles duringeach revolution of the rotor member, flow simultaneously proceedsthrough both of the diametrically opposed drilled passageways 66 to thetransverse drilling '63 and out through the discharge port 79 of thepump. When the centerline of the cylinder bores 14 reach the minor 56 ofthe cam-i ming surface 12, the trailing edge of the circular ports 42nove out of engagement with the arcuately shaped discharge port 52 tovalve off the cylinder bores 14 from both the suction and dischargeconnections of the pump. The ports 42 remain sealed oil from both of thesuction and discharge passages of the pump for the next 3 of rotation,or until their center lines have moved approximately 3 of rotation pastthe minor axis 56; and thereafter the leading edge of the circular ports52 moves past the trailing edge 53 of the port plate as to establish conrnunioationwith the suction of the pump. The ports 4-2 einain incommunication with the pump suction for a proximately 87 of rotationthereafter; and the entire cycle will thereafter be repeated withrespect to the diametrically opposed portion of the port plate 36.

As previously indicated, the amount of fluid discharged from the pumpcan be varied or regulated by rotation of the port plate as widi respectto the carrrning surface 12 of the casing member. Angular displacementof the port plate 36 with respect to the casing member A is acconplished by the structure best shown in FEGURE 3, and ch comprises aslide member 72 that is normally biased into its maximum flow producingposition by the coil spring The slide '72 is caused to angularlydisplace the port plate 3% in a direction reducing the output of thepump when a pressure exceeding approximately 1,500 psi. is supplied tothe piston 9%) which abuts the inner end of the slide member '72. Whenthe discharge pres: sure of the pump exceeds a proximately 1,500 psi,the spool valve structure 94 moves outwardly to compress spring 114sufficiently to cause land M2 to lap with respect to bore 95. the lands1% and N2 causes increasing control pressure to be delivered against thepiston which in turn causes the slide 72 to compress spring, 34'androtate the port plate 36. The port plate 36 will be rotated byincreasing amounts as the discharge pressure exceeds 1,500 psi; and whenapproximatel 1,650 psi. discharge pressure is reached, the'slide member72 will abut plug 88 and the port plate 35 will be rotated to its noflow producing position for the pump. As the discharge pressure of thepump falls below 1,650 psi. the reverse operation is produced; and itwill therefore be seen that the pump is capable of adjusting its rateoutput to correspond with the consumption of the hydraulic system towhich it is connected. The precise manner in which angular displacementof the port plate 36 reduces the displacement of the pump has previouslybeen set forth in detail and will not further be described.

During the discharge stroke of the cylinder bores 14, pressure flu dflows from individual ones of the cylinder bores 14, passes through thepassageway 133, past the ball check 142 into the recess 149 to bias theannular piston.

124 intoengagement with the slipper plate 136. When the individualcylinders 14 become communicated with the internal chamber it? of thepump, a slight reversal of flow causes the ball check 142 to engage itsseatand thereby maintain pressure within the recess 122. As pre- 7viously indicated, some of the fluid supplied to the recess 12?. passesthrough passage 14-8 to the annular grooves 144 and 146 to pressurizethe abutting surfaces of the annular piston 12 i and slipper plate'lfsto thereby reduce the direct bearing force between their slidingsurfaces. As previously indicated the hydraulic 'force tending toseparate the surfaces of the m nular piston and slipper plate is lessthan the pressure force on the inner end of the annular piston biasingit into engagement with the slipper plate 136 and which force in turn isgreater than the hydraulic pressure forces tending to separate the.valving surfaces 3 0 and 32 byan amount prevent ng excessive flowtherebetween. A continuing amount of leakage occurs out of the grooves144 and 145, as well as past the O-ringslild, 13%, and 132 which must bereplaced by flow, through passage 13% and check valve 1A2.- In orderthat at least one fiow passage 13% will at all times be communicatedThereafter variable leakage rates pass.

to pressure, three of the cylinder bores 14 in tne present instance areprovided with these passage and check valve structures.

The balancing piston structure of the present invention is not onlysimpler than that of prior art structures employing individual balancingpistons one for each or -re cylinder bores but has proven to have a muchgreater mechanical efiiciency, requiring considerably less horspower toproduce rotation of the rotor r ember B with respect to the casingmember A. The single annular piston of the present invention greatlyreduces 1e frictional forces between itself and its slipper clate;inasmuch as considerably less surface is swept by the singular annularpiston of the present invention than is re uired to be swept by aplurality of individual circular pr ons. What is more, the eifectivemoment are through whi these frictional resis nces are exerted upon theshaft is reduced to a prac ice-.1 minimum by the present invention. Afurther advantage is believed obtained by the s' annular pistonconstruction in that the fluid surface on the slipper elate 136 ismaintained by the single annular piston; While that in the p structuresis constantly changing in a manner can pressure fluid to be swe,;t frombetween t. e balanc'ug pistons and the slipper plate which they abut.

It will be apparent t at thc objects heretofore enumerated as as othersnave been achieved, and that an improved balancing piston arrangementbeen provided for fluid devices having end valving surfaces which arebiased apart by pressure fluid between the valving surfaces. While theinven n has been described in considerable detail, I do not h to belimited to the particular constructions shown and described, and it ismy 11 ention to cover hereby all novel adaptations, modifications andarrangements thereof which come within the practice of those sl; :vd inthe art to which the invention relates and which come within the scopeof the following claim.

I claim:

In a hydro-mechanical device: a casing member having an internal chamberwith opposite end walls through which an axis of rotation extends, arotor mounted for rotation in said chamber about said axis, one of saidend Walls of said casing havin a rotary val-ling surface wi h inlet andoutlet ports therein, and the other of said walls of said casing havinga smooth abutment surface thereon, one end of said rotor having acooperating rotary valving surface in sliding sealing engagement withsaid rotary valving surface of said casing, and the opposite end of saidrotor having an axially positioned recess therein opposite said smoothabutment surface on said casing, an annular balancing piston operativelyconnected to said rotor for rotary movement therewith and having aninner surface and an outer surface, said balancing piston being receivedin said recess and slidably and sealingly engaging the side of saidrecess for relative axial movement therebetween, the inner surface ofsaid balancing piston being disposed within said recess and the outersurface thereof slidably engaging the smooth abutment surface of saidcasing, passage means communicating a portion of said outer surface withsaid inner surface whereby pressure in said recess will be communicatedto said portion of said outer surface, a shaft rotatably mounted to theend walls of said casing for rotation about the axis, said shaft beingoperatively connected to said rotor for rotating the same and extendingaxially through said rotor, said recess and said balancing piston, saidrotor having at least one expansible chamber which communicates withsaid rotary valving surfaces and which expands and contracts duringrotation of said rotor, said rotor having a passageway communicatingsaid annular recess with said expansible chamber, a valve seat in saidlast named passageway, 21 ball check valve member adapted to be seatedsaid seat, said ball valve being so aranged in said last namedpassageway to be unseated by pressure flow to said recess from saidexpansible chamber and to be seated by pressure in said recess toprevent reverse flow to said expansible chamber, whereby said pressurein said recess acts on said piston inner face to bias the outer face ofsaid piston into sliding engagement with said smooth abutment surfaceand said rotor valving surface is biased against said casing valvingsurface by substantially constant pressure in said recess.

References Cited in the file of this patent UNiTED STATES PATENTS2,712,794 Humphreys July 12, 1955 2,871,798 Thoma Feb. 3, 1959 2,895,426Orshansky July 21, 1959 FOREIGN PATENTS 27,721 Great Britain Dec. 9,1911 of 1911

